The present invention relates to novel methods of preparing .alpha.-carbonylphosphine oxides and to novel .alpha.-hydroxyalkyl phosphine oxides.
1. Field of the Invention
.alpha.-Carbonylphosphine oxides are used as photoinitiators in polymerizable compositions.
2. Description of the Prior Art
EP-A 007,508 describes a process for the preparation of .alpha.-carbonylphosphine oxides by the reaction of carboxylic chlorides with alkoxyphosphines. Stoichiometric amounts of alkyl chlorides are formed as undesirable by-products in these reactions. Furthermore, some acid chlorides are obtainable only with difficulty. Thus, for example, o,o-disubstituted benzoic acids can be prepared by complicated means only, ie, by haloform reaction of the corresponding acetophenones (EP-A 046,194). However, these benzoic acids are particularly desirable starting materials for industrially highly significant photoinitiators.
The reaction of disubstituted phosphine oxides with aldehydes and ketones in the presence of bases to form .alpha.-hydroxyalkyl phosphine oxides is described in J. Am. Chem. Soc., 79, 424 (1957). Inter alia, compounds which are phenyl-substituted on the .alpha.-carbon atom are prepared by this method.
The preparation of some para-substituted .alpha.-hydroxybenzyldiphenyl phosphine oxides from diphenyl chlorophosphine, an aqueous mineral acid, and an aromatic aldehyde is described in J. Org. Chem., 34, 748 (1969), in which the para-substituents include methyl, methoxy, chlorine, and the nitro group.
There has also been disclosed a method of using tert-butylhydroperoxide as a selective oxidizing agent for aliphatic and cycloaliphatic secondary alcohols in the presence of vanadyl acetylacetonate, as disclosed in Tetrahedron Lett., 24, 5009 (1983).
It is an object of the invention to find a novel process which produces .alpha.-carbonylphosphine oxides using readily obtainable compounds as starting point. Another object is to provide a process which makes it possible to prepare the particularly interesting primary stages, namely .alpha.-hydroxyphosphine oxides carrying a 2,6-disubstituted phenyl radical on the .alpha.-carbon atom and to convert said products to .alpha.-carbonylphosphine oxides.